Pharmacological enhancement of cortical inhibition affects lateral interactions in human vision

Abstract

Perceptual facilitation, a decrease in detection threshold for low-contrast Gabor patches (GPs), occurs when a low-contrast GP is flanked by collinearly oriented high-contrast GPs. It was suggested earlier that a spatial architecture of excitation and inhibition is the basis of these lateral interactions. The GABA_AR agonist, lorazepam, enhances the cortical inhibition and thus disrupts the balance between inhibition relative to excitation (I/E) that has been implicated in plasticity regulation and has recently been shown to affect visual perception. Here we recorded Event-Related Potentials (ERPs) in healthy volunteers to study the effects of pharmacological interference with the I/E balance on lateral interactions. Our previous studies provided evidence for N1 peak amplitude modulation by collinear context (Sterkin et al., 2008). Moreover, we also found a robust correlation between N1 peak amplitude and the backward masking effect (Sterkin et al., 2007). We measured the latency and amplitude of N1 elicited by a foveal GP and collinear flankers separated by 1.5 or 3 wavelengths before and after the uptake of lorazepam. As expected, lateral interactions induced behavioral suppression for the separation of 1.5 wavelengths and facilitation for 3 wavelengths. However, facilitation was significantly abolished after lorazepam uptake and the N1 amplitude was robustly decreased for the separation of 3 wavelengths, reminiscent of the backward masking effects reported earlier. Surprisingly, reaction time was shortened after the uptake of lorazepam. These results imply that both behavioral manifestation and the neuronal correlates of lateral interactions are modulated by the pharmacologically induced increase of cortical inhibition. Specifically, this may suggest a mechanism of noise reduction that promotes faster and unambiguous processing. Thus, our findings support a critical role for the I/E balance in maintaining context effects in the visual cortex. This study was supported by the National Institute of Psychobiology in Israel and the Israel Science Foundation.